Research during the past 10-15 years has provided basic information on the anatomy, pharmacology, neurochemistry and electrophysiology of serotonin-containing neurons in the mammalian CNS. In combination with behavioral and physiological studies, this has produced a number of general hypotheses regarding the functional significance of brain serotonin. Experiments in the present proposal, are designed to more directly test some of these general hypotheses, to test some of our own more specific hypotheses, and to provide basic background information on the responsivity of this system across a variety of situations. These studies will examine raphe unit activity in conjunction with behavior in freely moving cats. Our basic sample of unit activity will be from the dorsal raphe nucleus, but we will also attempt to obtain data from raphe pallidus. Experiments are proposed in four general areas: sleep, arousal and behavior inhibition; feeding and dietary manipulations; hallucinogenic drugs; and explorations of changes in raphe unit activity in response sensory stimuli and motivational/behavioral manipulations.